This invention relates to a steam injection system for use in a gas turbine engine and, in particular, to a steam injection control system for preventing unwanted moisture and solid particulates from being ingested into the gas turbine with the injected steam.
The value of injecting steam into a gas turbine engine for increasing the engine efficiency has been known for quite some time. A joint paper entitled Maximum Steam Injection in Gas Turbines was presented at the South Power Generation Conference in 1972 by W. H. Day and P. H. Kydd outlining some of the effects of controlled steam injection. Steam injection gas turbine engines have been developed for cogenerating both electrical energy and steam. The proper conditioning and control of the steam used for steam injection in a gas turbine is, however, difficult to obtain. Moisture can collect in the injection system along with particulates which are carried by the injected steam into the turbine. Dirt and moisture that are introduced into the engine can damage the rotating components of the machine. Also of concern is the danger posed by the continued injection of steam into the combustor in the event the gas turbine engine is tripped during an emergency shut down. Under these conditions, the turbine is allowed to coast down and the compressor bleed valves are opened.
Hamill et al in U.S. Pat. No. 4,597,256 describe a method of terminating the flow of injection steam to the combustor of a gas turbine. A complex counter flow heat exchanger unit is employed in this system for generating the injected steam which includes a superheater section, an evaporator section, and an economizer section. A valve is mounted between the superheater and evaporator sections which is closed at the end of the steam injection cycle, but prior to engine shut down. The engine is allowed to run for a short period of time after the steam flow has been terminated to insure that any steam that might be trapped in the injection line in front of the valve will be consumed and thus prevented from condensing inside the lines. The Hamill et al system, however, is incapable of protecting the engine from moisture or other contaminants during start up or emergency shut downs.